Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$211.72	10.698%	$234.3698	$234.37	$234.35	$234.40
Purchase #2	$174.48	9.421%	$190.9178	$190.92	$190.90	$190.90
Purchase #3	$138.58	5.757%	$146.5581	$146.56	$146.55	$146.60
Purchase #4	$49.55	13.810%	$56.3929	$56.39	$56.40	$56.40
Purchase #5	$86.78	9.313%	$94.8618	$94.86	$94.85	$94.90
Purchase #6	$136.34	10.863%	$151.1506	$151.15	$151.15	$151.20
Purchase #7	$102.65	13.632%	$116.6432	$116.64	$116.65	$116.60
7 purchase totals =	$900.10		$990.8942	$990.89	$990.85	$991.00